The field of this invention is one-trip completion systems, which allow for zone isolation and production using a technique for expansion of screens and isolators, preferably in open hole completions.
Typically zonal isolation is desirable in wells with different pressure regimes, incompatible reservoir fluids, and varying production life. The typical solution to this issue in the past has been to cement and perforate casing. Many applications further required gravel packing adding an extra measure of time and expense to the completion. The cemented casing also required running cement bond logs to insure the integrity of the cementing job. It was not unusual for a procedure involving cemented casing, gravel packing and zonal isolation using packers to take 5-20 days per zone and cost as much or over a million dollars a zone. Use of cement in packers carried with it concerns of spills and extra trips into the well. Frequently fracturing techniques were employed to increase well productivity but cost to complete was also increased. Sand control techniques, seeking to combine gravel packing and fracturing, also bring on risks of unintended formation damage, which could reduce productivity.
In open hole completions, gravel packing was difficult to effectively accomplish although there were fewer risks in horizontal pay zones. The presence of shale impeded the gravel packing operation. Proppant packs were used in open hole completions, particularly for deviated or horizontal open hole wells. Proppant packing involved running a screen in the hole and pumping proppants outside of it. Proppants such as gravel or ceramic beads were effective to control cave-ins but still allowed water or gas coning and breakthroughs. Proppant packs have been used between activated isolation devices such as external casing packers in procedures that were complex, time consuming, and risky. More recently, a new technique which is the subject of a co-pending patent application also assigned to Baker Hughes Incorporated a refined technique has been developed wherein a proppant pack is delivered on both sides of a non-activated annular seal. In this technique the seal can thereafter be activated against casing or open hole. While this technique involved improved zonal isolation, it was still costly and involved complex delivery tools and techniques for the proppant.
Shell Oil Company has disclosed more recently, techniques for expansion of slotted liners using force driven cones. Screens have been mechanically expanded, in an effort to eliminate gravel packing in open hole completions. The use of cones to expand slotted liners suffered from several weaknesses. The structural strength of the screens or slotted liners being expanded suffered as a tradeoff to allow the necessary expansion desired. When placed in service such structures could collapse at differential pressures on expanded screens of as low as 2-300 pounds per square inch (PSI). Expansion techniques suffered from other shortcomings such as the potential for rupture of a tubular or screen upon expansion. Additionally, where the well bore is irregular the cone expander will not apply uniform expansion force to compensate for void areas in the well bore. This can detract from seal quality. Cone expansion results in significant longitudinal shrinkage, which potentially can misalign the screen being expanded from the pay zone, if the initial length is sufficiently long. Due to longitudinal shrinkage, overstress can occur particularly when expanding from bottom up. Cone expansions also require high pulling forces in the order of 250,000 pounds. Slotted liner is also subject to relaxation after expansion. Cone expansions can give irregular fracturing effect, which varies with the borehole size and formation characteristics.
Accordingly the present invention has as its main objective the ability to replace traditional cemented casing completion procedures. This is accomplished by running isolators in pairs for each zone to be produced with a screen in between. The screen and isolators are delivered in a single trip and expanded down hole using an inflatable device to preferably expand the isolators. The screens can also be similarly expanded using an inflatable tool or by virtue of mechanical expansion, depending on the application. Each zone can be isolated in a single trip. The completion assembly and the expansion tool can selectively be run in together or on separate trips. These and other features of the invention can be more readily understood by a review of the description of the preferred embodiment, which appears below.
A completion technique to replace cementing casing, perforating, fracturing, and gravel packing with an open hole completion is disclosed. Each zone to be isolated by the completion assembly features a pair of isolators, which are preferably tubular with a sleeve of a sealing material such as an elastomer on the outer surface. The screen is preferably made of a weave in one or more layers with a protective outer, and optionally an inner, jacket with openings. The completion assembly can be lowered on rigid or coiled tubing which, internally to the completion assembly, includes the expansion assembly. The expansion assembly is preferably an inflatable design with features that provide limits to the delivered expansion force and/or diameter. A plurality of zones can be isolated in a single trip.